Thermal Reflector Device for Semiconductor Fabrication Tool

ABSTRACT

A system and apparatus for thermal treatment of a substrate with improved thermal uniformity is provided. In some embodiments, the system includes a heating element, a substrate-retaining element operable to retain a substrate, and a reflective structure operable to direct thermal energy of the heating element towards the substrate retained in the substrate-retaining element. The reflective structure includes a textured portion wherein a texture of the textured portion is configured to direct the thermal energy towards the retained substrate. In some such embodiments, the texture includes a roughened irregular surface configured to direct the thermal energy towards the retained substrate. In some such embodiments, the texture includes a plurality of circumferential ridge structures configured to direct the thermal energy towards the retained substrate.

PRIORITY DATA

This application claims the benefit of U.S. Prov. App. No. 62/288,663entitled “Thermal Reflector Device for Semiconductor Fabrication Tools,”filed Jan. 29, 2016, herein incorporated by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. In the course of IC evolution, functional density (i.e., thenumber of interconnected devices per chip area) has generally increasedwhile geometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. However, such scaling down has also beenaccompanied by increased complexity in design and manufacturing ofdevices incorporating these ICs, and, for these advances to be realized,similar developments in device design are needed.

For example, epitaxy is one technique for depositing material used inthe fabrication of integrated circuits that is ripe for improvement.Epitaxy may be used to grow semiconductor crystals as well as othercrystalline structures. In a conventional vapor-phase epitaxial process,a target material is heated, and a semiconductor-containing gas issupplied. If the environment is properly maintained, the semiconductorprecipitates out of the gas and on to the target in a controlled manner.In particular, the rate of precipitation/deposition depends on thesurface temperature of the target material, as well as the supply rateof the gas or gasses and pressure within the epitaxial chamber. Epitaxyis capable of producing layers of highly uniform thickness; howeverminute deviations that may be perfectly acceptable in one technology maybe critical defects once the design node shrinks. Accordingly, whileconventional systems and techniques of epitaxial deposition have beenadequate for previous designs, they may not be able to meet the needs ofthe next generation of integrated circuits. In order to continue to meetever-increasing design requirements, further advances are needed in thisarea and others.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a schematic view of a fabrication system according to variousaspects of the present disclosure.

FIG. 2 is a plot of observed results of an epitaxial process accordingto various aspects of the present disclosure.

FIG. 3 is a perspective view of a top reflector according to someembodiments of the present disclosure.

FIG. 4 is a cross-sectional view of a portion of a top reflector havingcircumferential ridges of varying height according to some embodimentsof the present disclosure.

FIG. 5 is a cross-sectional view of a portion of a top reflector havingcircumferential ridges of varying width according to some embodiments ofthe present disclosure.

FIG. 6 is a perspective view of a top reflector according to someembodiments of the present disclosure.

FIG. 7 is a perspective view of a top reflector according to someembodiments of the present disclosure.

FIG. 8 is a perspective view of a bottom reflector according to someembodiments of the present disclosure.

FIG. 9 is a cross-sectional view of a portion of a bottom reflectorhaving circumferential ridges of varying height according to someembodiments of the present disclosure.

FIG. 10 is a cross-sectional view of a portion of a bottom reflectorhaving circumferential ridges of varying width according to someembodiments of the present disclosure.

FIG. 11 is a perspective view of a bottom reflector according to someembodiments of the present disclosure.

FIG. 12 is a perspective view of a bottom reflector according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to IC device manufacturing and,more particularly, to a system for thermal treatment of a substrate withimproved thermal uniformity.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIG. 1 is a schematic view of a fabrication system 100 according tovarious aspects of the present disclosure. The principles of the presentdisclosure apply equally across a wide array of fabrication tools, andthe fabrication system 100 may be representative of an epitaxial tool,an annealing tool, and/or any other integrated circuit fabrication toolin which the temperature of a workpiece or substrate affects the qualityof the results. FIG. 1 has been simplified for the sake of clarity andto better illustrate the concepts of the present disclosure.

In some embodiments, the fabrication system 100 is operable to performan epitaxial process and thereby deposit a crystalline, polycrystalline,and/or amorphous material on a substrate 102. Suitable substrates 102encompass any workpiece used in semiconductor fabrication. For example,the substrate 102 may include bulk silicon. In various examples, thesubstrate 102 may comprise an elementary (single element) semiconductor,such as silicon or germanium in a crystalline structure; a compoundsemiconductor, such as silicon germanium, silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; or combinations thereof. The substrate 102 may alsohave a silicon-on-insulator (SOI) structure and thus may include aninsulator such as a semiconductor oxide, a semiconductor nitride, asemiconductor oxynitride, a semiconductor carbide, and/or other suitableinsulator materials. SOI substrates are fabricated using separation byimplantation of oxygen (SIMOX), wafer bonding, and/or other suitablemethods. In some embodiments, the substrate 102 is a mask substrate andincludes non-semiconductor materials such as quartz, LTEM glass, siliconcarbide, silicon oxide, and/or titanium oxide.

The substrate 102 may be retained in a susceptor 104 within a centralchamber 106 of the fabrication system 100 for processing. Atmosphericcontrols, including filtering, maintain an environment with extremelylow levels of particulates and airborne molecular contamination (“AMC”),both of which may damage a substrate 102. By creating a microenvironmentwithin the central chamber 106, the epitaxial process can be performedin a cleaner environment than the surrounding facilities. The sealedconstruction of the central chamber 106 may also help to maintainpressure or temperature and to contain process gases.

Within this central chamber 106, heating of the substrate 102 forepitaxy and/or other processes may be performed in part by one or moreheating elements 108. Heating elements 108 may include infrared lamps,radiant heating tubes, burners, and/or any other suitable heatingelement. In some embodiments, the heating elements 108 may directed atthe front surface (e.g., the surface undergoing epitaxial growth and theuppermost surface as shown in FIG. 1) of the substrate 102, the backsurface of the substrate 102, or a combination thereof. The fabricationsystem may include reflectors, such as top reflector 110 and bottomreflector 112, to direct thermal energy towards the substrate 102. Thereflectors may be particularly beneficial for heating elements 108 thatare not directional.

In addition to or as an alternative to the heating elements 108, thecentral chamber 106 may include one or more induction heating coilsdisposed near to the substrate. In some embodiments, the heating coilsare integrated into the susceptor 104 and transfer energy through theback surface of the substrate 102, although the induction heating coilsmay also be separate from the susceptor 104 and direct thermal energy toany surface of the substrate 102.

During an exemplary epitaxy process, the heating elements 108 heat thesubstrate 102 to a suitable temperature (about 650° C. in alow-temperature example and about 1200° C. in a high-temperatureexample). Once the substrate 102 is heated, various gases are providedon the substrate 102. In an example, a semiconductor-containingprecursor gas (e.g., SiH₄, Si₂H₆, SiHCl₃, etc.) is provided from aninlet 114 across the front surface of the substrate 102. A second gas, acarrier gas, (e.g., H₂, N₂, etc.) is provided around the substrate 102.In some examples, the carrier gas is provided up through ports in thesusceptor 104. The gasses react, and the semiconductor of the precursorgas is deposited on the front surface of the substrate 102 to form anorderly crystalline structure. The carrier gas may catalyze the reactionof the precursor gas and may carry the resultant products away from thesubstrate 102. Remaining gases and the resulting gaseous products areexhausted through an exhaust port 116.

Referring to FIG. 2, it has been determined through experimentation thatin many fabrication systems 100, the substrate 102 is heated unevenlydespite a uniform distribution of heating elements 108. FIG. 2 is a plot200 of observed results of an epitaxial process according to variousaspects of the present disclosure. Axis 202 represents normalizedthickness of an epitaxially-grown material formed on the substrate 102measured at the front surface, and axis 204 indicates distance along adiameter of the substrate 102 (indicated by arrow 118 of FIG. 1) atwhich the thickness was measured.

Curve 206 represents heating using a first type of fabrication system100 and shows that the growth rate upon the substrate 102 is notuniform. For example, the measured thickness in a circumferential regionof the substrate 102 (indicated by markers 210) may be significantlyless than the thickness at the center of the substrate 102 (indicated bymarker 212). Furthermore, the thickness throughout the circumferentialregion may vary significantly (i.e., the thickness at the 3 o'clockposition may vary from the thickness at the 9 o'clock position). In someapplications, this is caused by temperature variability across thesurface of the substrate 102 that causes process variations includingthe differences in thickness. These process variations may reduce yieldin some parts of the substrate 102.

In contrast, curve 208 represents heating using a fabrication system 100that includes improved reflectors described in more detail below. As isevident from the curve 208, the thickness of the epitaxial material onthe circumferential region of the substrate 102 is closer to thethickness at the center of the substrate. This indicates that thetemperature during the epitaxial process is more uniform between thecenter and circumferential region of the substrate 102. Whiletemperature values at intermediate locations on the substrate 102 may behigher than those of curve 206, resulting in greater thickness of theepitaxial material, these higher temperatures may or may not affectyield depending on the process being performed. In some examples, excessepitaxial material is easily removed by chemical mechanicalpolishing/planarization (CMP). Even when epitaxial material is not soeasily removed, temperatures at intermediate locations may be easier tocontrol than temperatures along the edge of the wafer. Accordingly, theimproved reflectors described with reference to FIGS. 3-12 havedemonstrated significant reductions in temperature variability andsignificant improvements in yield.

FIG. 3 is a perspective view of a top reflector 300 according to someembodiments of the present disclosure. The top reflector 300 is suitablefor use as the top reflector 110 of the fabrication system 100 of FIG. 1and/or any other suitable fabrication tool. For clarity, an outerportion 302 of the reflector 300 is represented as transparent to betterillustrate an inner portion 304. In some embodiments, the top reflector300 is structured so that thermal energy from heating elements 108 isemitted between the outer portion 302 and the inner portion 304. In somesuch embodiments, the heating elements 108 extend through holes in theouter portion 302 so that a portion of each heating element 108 thatproduces the energy is disposed between the outer portion 302 and theinner portion 304. Exemplary rays 306 of thermal energy emitted by theheating elements are shown and represent radiant heat such as infraredor other thermal radiation and/or any other type of emitted energy.

The inner portion 304 of the top reflector 300 has a round body 308extending from an upper flange 310. The round body 308 is designed witha shape and a surface pattern so that to reflect thermal energy from theheating elements 108 towards the substrate 102, in particular, towardsthe circumference of the substrate 102. In the present embodiment, theround body 308 is a substantially cylindrical body (still referred to as308), which may be made of any suitable material such as silver, gold,and/or copper, is configured to reflect the thermal energy from theheating elements 108. Furthermore, in the illustrated embodiment, theinner portion 304 has a textured region 312 along the length of thesubstantially cylindrical body 308. The texture of the textured region312 may be configured so that reflected thermal energy is directedtowards the substrate 102 and, in particular, towards the circumferenceof the substrate 102. Compared to a conventional design, the topreflector 300 with the textured region 312 may reflect more thermalenergy towards the edge of the substrate 102 and may produce moreuniform substrate heating. In these ways and others, the top reflector300 having the textured region 312 provides greater control over wherethe reflected energy falls on the substrate 102 than a conventional topreflector.

To achieve this, the textured region 312 may include one or morecircumferential ridges 314 aligned with the circumference of thecylindrical body 308 that extend any suitable depth into and/or out ofthe outermost surface of the inner portion 304. The circumferentialridges 314 are enlarged to provide clarity, and in various exemplaryembodiments, the ridges 314 have a peak-to-trough height of betweenabout 0.1 mm to about 2 mm. The particular height may be selected tocontrol where the reflected thermal energy is received on the substrate102. The amount of reflected thermal energy and where it falls on thesubstrate 102 may also be controlled by the amount of the substantiallycylindrical body 308 that is textured to produce the textured region 312and where the textured region 312 is located along the cylindrical body308. For example, in some embodiments, the body 308 includes anuntextured portion between the upper flange 310 and the textured region312. In other embodiments, the textured region 312 extends completely tothe upper flange 310.

The circumferential ridges 314 may be formed by any suitable process orprocesses. In some examples, the ridges 314 are formed by mechanicalmeans such as cutting or forming (e.g., bending, tucking, stretching,etc.), which may be followed by polishing. In some examples, the ridges314 are formed by chemical means such as chemical etching, which may beperformed as part of a polishing process. In further examples, theridges 314 are formed by a combination of both mechanical and chemicalmeans.

While the circumferential ridges 314 in the embodiments of FIG. 3 areuniform in peak-to-trough height and trough-to-trough width, in otherembodiments, the ridges 314 vary along the textured region 312. Byvarying the ridge 314 shape, the angle of the surfaces of the ridge 314can be tuned in order to control where energy reflected by the ridge 314falls on the substrate 102. For example, FIG. 4 is a cross-sectionalview of a portion of a top reflector 400 having circumferential ridges314 of varying height according to some embodiments of the presentdisclosure. The top reflector 400 may be substantially similar to thetop reflector 300 of FIG. 3 and is suitable for use as the top reflector110 of the fabrication system 100 of FIG. 1 and/or any other suitablefabrication tool. An outer portion of the reflector 400 is omitted tobetter illustrate an inner portion 304 but may be substantially similarto the outer portion 302 of FIG. 3.

As can be seen, the peak-to-trough height of the ridges 314 varies alongthe textured region 312. In the illustrated embodiment, ridges 314 nearthe top of the top reflector 400 have a greater peak-to-trough heightthan ridges 314 near the bottom of the top reflector 400, although thisis merely exemplary and in further embodiments, the opposite is true(i.e., ridges 314 near the bottom of the top reflector 400 have agreater peak-to-trough height than ridges 314 near the top of the topreflector 400).

FIG. 5 is a cross-sectional view of a portion of a top reflector 500having circumferential ridges 314 of varying width according to someembodiments of the present disclosure. The top reflector 500 may besubstantially similar to the top reflectors 300 and 400 of FIGS. 3 and4, respectively, and is suitable for use as the top reflector 110 of thefabrication system 100 of FIG. 1 and/or any other suitable fabricationtool. An outer portion of the reflector 400 is omitted to betterillustrate an inner portion 304 but may be substantially similar to theouter portion 302 of FIG. 3.

As can be seen, the trough-to-trough width of the ridges 314 variesalong the textured region 312. In the illustrated embodiment, ridges 314near the top of the top reflector 500 have a narrower width than ridges314 near the bottom of the top reflector 500, although this is merelyexemplary, and in further embodiments, the opposite is true (i.e.,ridges 314 near the bottom of the top reflector 500 have a narrowerwidth than ridges 314 near the top of the top reflector 500).

Of course, it is understood that features may be combined from any ofthe exemplary top reflectors 300, 400, and 500, and no particularfeature is required for any particular embodiment.

In the embodiments of FIGS. 3-5, the textured region 312 includes aseries of circumferential ridges 314 that wrap around substantiallycylindrical body 308. Additionally or alternatively, some or all of thetextured region 312 may have a roughened texture configured to controlreflected thermal energy. FIG. 6 is a perspective view of a topreflector 600 according to some embodiments of the present disclosure.The top reflector 600 is suitable for use as the top reflector 110 ofthe fabrication system 100 of FIG. 1 and/or any other suitablefabrication tool. For clarity, an outer portion 302 of the reflector 600is represented as transparent to better illustrate an inner portion 304.The outer portion 302 may be substantially similar to that described inFIG. 3 and may be structured so that thermal energy from heatingelements 108 is emitted between the outer portion 302 and the innerportion 304. In some such embodiments, the heating elements 108 extendthrough holes in the outer portion 302 so that a portion of each heatingelement 108 that produces the energy is disposed between the outerportion 302 and the inner portion 304. Exemplary rays 306 of thermalenergy emitted by the heating elements are shown and represent radiantheat such as infrared or other thermal radiation and/or any other typeof emitted energy.

Except where noted, the inner portion 304 may also be substantiallysimilar to that described in FIG. 3 and may have a substantiallycylindrical body 308 extending from an upper flange 310. Thesubstantially cylindrical body 308, which may be made of any suitablematerial such as silver, gold, and/or copper, is configured to reflectthe thermal energy from the heating elements 108. The inner portion 304includes a textured region 312 configured so that reflected thermalenergy is directed towards the substrate 102 and, in particular, towardsa circumferential region of the substrate 102. To achieve this, thetextured region 312 includes a roughened portion 602 configured tocontrol the reflected energy. However, in contrast to the topography ofthe circumferential ridges 314, the roughened portion 602 of thetextured region 312 has an irregular surface with peaks and valleys withrandom or semi-random amplitude and/or frequency. Alternatively, theroughened portion 602 of the textured region 312 may be designed to havea surface with peaks and valleys with orderly, random, or semi-randomamplitude and/or frequency so that reflected thermal energy is directedtowards the substrate 102 and, in particular, towards a circumferentialregion of the substrate 102.

In some embodiments, the roughened portion 602 includes a surfacepattern having irregular dot peaks 604 designed such that the rays 306of thermal energy are directed toward the substrate 102. The irregulardot peaks of the surface pattern in the roughened portion have peakheight, dot size, dot shape, dot density, dot distribution or acombination thereof varying from peak to peak irregularly. In someexamples, the irregular dot peaks have a peak height varying from peakto peak in irregular distribution, tuned to effectively direct the rays306 of thermal energy toward the substrate 102. In some examples, theirregular dot peaks have a dot size varying from peak to peak inirregular distribution, tuned to effectively direct the rays 306 ofthermal energy toward the substrate 102. In some examples, the irregulardot peaks have an irregular peak location distribution tuned toeffectively direct the rays 306 of thermal energy toward the substrate102. In some examples, the irregular dot peaks have a dot shape (in atop view) varying from peak to peak (such as varying from a round shapeto a square shape, a polygon or other shape) and tuned to effectivelydirect the rays 306 of thermal energy toward the substrate 102. Infurtherance of the examples, the dot shape is asymmetric, wherein theupper half and the lower half of a dot peak are different from eachother, such as one dot peak 604 illustrated in the bottom right cornerof FIG. 6. In some embodiments, the irregular dot peaks have anirregular three-dimensional (3D) profile varying from peak to peak andtuned to effectively direct the rays 306 of thermal energy toward thesubstrate 102.

The roughened portion 602 may have any suitable degree of roughness andmay be substantially rougher than the remainder of the cylindrical body308. The roughness may be uniform throughout the roughened portion 602or may be graded. In some embodiments, the roughened portion 602 has agreater degree of roughness near the top of the top reflector 600 thannear the bottom of the top reflector 600, although this is merelyexemplary and in further embodiments, the opposite is true (i.e., theroughened portion 602 is less rough near the top of the top reflector600 than near the bottom of the top reflector 600).

The roughened portion 602 may be formed by any suitable process orprocesses. In some examples, the roughened portion 602 is formed bymechanical means such as abrading and/or thermal deformation, while insome examples, the roughened portion 602 is formed by chemical meanssuch as chemical etching. In further examples, the roughened portion 602is formed by a combination of both mechanical and chemical means.

Of course, ridges and surface roughening are not mutually exclusive. Insome embodiments, both techniques are used to control where reflectedenergy falls on the substrate 102. FIG. 7 is a perspective view of a topreflector 700 according to some embodiments of the present disclosure.The top reflector 700 is suitable for use as the top reflector 110 ofthe fabrication system 100 of FIG. 1 and/or any other suitablefabrication tool. For clarity, an outer portion 302 of the reflector 700is represented as transparent to better illustrate an inner portion 304.The outer portion 302 may be substantially similar to that described inFIG. 3 and may be structured so that thermal energy from heatingelements 108 is emitted between the outer portion 302 and the innerportion 304. In some such embodiments, the heating elements 108 extendthrough holes in the outer portion 302 so that a portion of each heatingelement 108 that produces the energy is disposed between the outerportion 302 and the inner portion 304. Exemplary rays 306 of thermalenergy emitted by the heating elements are shown and represent radiantheat such as infrared or other thermal radiation and/or any other typeof emitted energy.

Except where noted, the inner portion 304 may also be substantiallysimilar to that described in FIG. 3 and may have a substantiallycylindrical body 308 extending from an upper flange 310. Thesubstantially cylindrical body 308, which may be made of any suitablematerial such as silver, gold, and/or copper, is configured to reflectthe thermal energy from the heating elements 108. The inner portion 304includes a textured region 312 configured so that reflected thermalenergy is directed towards the substrate 102 and, in particular, towardsa circumferential region of the substrate 102. The textured region 312includes circumferential ridges 314 substantially as described in FIGS.3-5 with a roughened texture substantially similar to the roughenedportion 602 of FIG. 6. Together, the ridges and the roughened textureare configured to direct the emitted energy to specific locations on thesubstrate 102 (e.g., a circumferential region near the circumferentialperimeter of the substrate 102).

As with the top reflector, the bottom reflector 112 may include atextured region to control where reflected thermal energy falls on thesubstrate 102. FIG. 8 is a perspective view of a bottom reflector 800according to some embodiments of the present disclosure. The bottomreflector 800 is suitable for use as the bottom reflector 112 of thefabrication system 100 of FIG. 1 and/or any other suitable fabricationtool. For clarity, an outer portion 802 of the bottom reflector 800 isrepresented as transparent to better illustrate an inner portion 804. Insome embodiments, the bottom reflector 800 is structured so that thermalenergy from heating elements 108 is emitted between the outer portion802 and the inner portion 804. In some such embodiments, the heatingelements 108 extend through holes in the outer portion 802 so that aportion of each heating element 108 that produces the energy is disposedbetween the outer portion 802 and the inner portion 804.

In the present embodiment, the inner portion 804 of the bottom reflector800 has a substantially cylindrical body 806 and a substantiallyfrustoconical segment 808 that flares outward extending from thesubstantially cylindrical body 806. The body 806 and the frustoconicalsegment 808, which may be made of any suitable material such as silver,gold, and/or copper, may each be configured to reflect the thermalenergy from the heating elements 108. While the body 806 may betextured, in the illustrated embodiment, it is the frustoconical segment808 that contains a textured region 810. The texture of the texturedregion 810 may be configured so that reflected thermal energy isdirected towards the substrate 102 from the bottom and, in particular,towards the circumferential region of the substrate 102. Compared to asmooth configuration, the bottom reflector 800 with the textured region810 may reflect more thermal energy towards the substrate 102 and mayproduce more uniform substrate heating.

The texture of the textured region 810 may include a series ofcircumferential ridges 812 that extend any suitable depth into and/orout of the outermost surface of the inner portion 804. The ridges 812are enlarged to provide clarity, and in various exemplary embodiments,the ridges 812 have a peak-to-trough height of between about 0.1 mm toabout 2 mm. The particular height may be selected to control where thereflected thermal energy is received on the substrate 102. The amount ofreflected thermal energy and where it falls on the substrate 102 mayalso be controlled by the amount of the frustoconical segment 808 thatis textured to produce the textured region 810 and where the texturedregion 810 is located. For example, in some embodiments, thefrustoconical segment 808 includes an untextured portion between thesubstantially cylindrical body 806 and the textured region 810, while inother embodiments, the textured region 810 extends completely to thecylindrical body 806.

The circumferential ridges 812 may be formed by any suitable process orprocesses. In some examples, the ridges 812 are formed by mechanicalmeans such as cutting or forming (e.g., bending, tucking, stretching,etc.), which may be followed by polishing. In some examples, the ridges812 are formed by chemical means such as chemical etching, which may beperformed as part of a polishing process. In further examples, theridges 812 are formed by a combination of both mechanical and chemicalmeans.

In some embodiments, the circumferential ridges 812 vary along thetextured region 810. For example, FIG. 9 is a cross-sectional view of aportion of a bottom reflector 900 having circumferential ridges 812 ofvarying height according to some embodiments of the present disclosure.The bottom reflector 900 may be substantially similar to the bottomreflector 800 of FIG. 8 and is suitable for use as the bottom reflector112 of the fabrication system 100 of FIG. 1 and/or any other suitablefabrication tool. An outer portion of the reflector 800 is omitted tobetter illustrate an inner portion 804 but may be substantially similarto the outer portion 802 of FIG. 8.

As can be seen, the peak-to-trough height of the ridges 812 varies alongthe textured region 810. In the illustrated embodiment, ridges 812 nearthe top of the bottom reflector 900 have a greater peak-to-trough heightthan ridges 812 near the bottom of the bottom reflector 900, althoughthis is merely exemplary, and in further embodiments, the opposite istrue (i.e., ridges 812 near the bottom of the bottom reflector 900 havea greater peak-to-trough height than ridges 812 near the top of thebottom reflector 900).

FIG. 10 is a cross-sectional view of a portion of a bottom reflector1000 having circumferential ridges 812 of varying width according tosome embodiments of the present disclosure. The bottom reflector 1000may be substantially similar to the bottom reflectors 800 and 900 ofFIGS. 8 and 9, respectively, and is suitable for use as the bottomreflector 112 of the fabrication system 100 of FIG. 1 and/or any othersuitable fabrication tool. An outer portion of the reflector 800 isomitted to better illustrate an inner portion 804 but may besubstantially similar to the outer portion 802 of FIG. 8.

As can be seen, the trough-to-trough width of the ridges 812 variesalong the textured region 810. In the illustrated embodiment,circumferential ridges 812 near the top of the bottom reflector 1000have a narrower width than ridges 812 near the bottom of the bottomreflector 1000, although this is merely exemplary, and in furtherembodiments, the opposite is true (i.e., ridges 812 near the bottom ofthe bottom reflector 1000 have a narrower width than ridges 812 near thetop of the bottom reflector 1000).

Of course, it is understood that features may be combined from any ofthe exemplary bottom reflectors 800, 900, and 1000, and no particularfeature is required for any particular embodiment.

Additionally or in the alternative, some or all of the textured region810 may have a roughened texture configured to control reflected thermalenergy. FIG. 11 is a perspective view of a bottom reflector 1100according to some embodiments of the present disclosure. The bottomreflector 1100 is suitable for use as the bottom reflector 112 of thefabrication system 100 of FIG. 1 and/or any other suitable fabricationtool. For clarity, an outer portion 802 of the reflector 1100 isrepresented as transparent to better illustrate an inner portion 804.The outer portion 802 may be substantially similar to that described inFIG. 8 and may be structured so that thermal energy from heatingelements 108 is emitted between the outer portion 802 and the innerportion 804. In some such embodiments, the heating elements 108 extendthrough holes in the outer portion 802 so that a portion of each heatingelement 108 that produces the energy is disposed between the outerportion 802 and the inner portion 804.

Except where noted, the inner portion 804 may also be substantiallysimilar to that described in FIG. 8 and may have a substantiallycylindrical body 806 and a substantially frustoconical segment 808 thatflares outward extending from the substantially cylindrical body 806.The body 806 and the frustoconical segment 808, which may be made of anysuitable material such as silver, gold, and/or copper, may each beconfigured to reflect the thermal energy from the heating elements 108.While the body 806 may be textured, in the illustrated embodiment, it isthe frustoconical segment 808 that contains a textured region 810. Thetextured region 812 may include a roughened portion 1102 configured tocontrol the reflected energy. However, in contrast to the topography ofthe circumferential ridges 812, the roughened portion 1102 of thetextured region 812 has an irregular surface with peaks and valleys withrandom or semi-random amplitude and/or frequency.

The roughened portion 1102 may have any suitable degree of roughness andmay be substantially rougher than the remainder of the frustoconicalsegment 808 and/or cylindrical body 806. The roughness may be uniformthroughout the roughened portion 1102 or may be graded. In someembodiments, the roughened portion 1102 has a greater degree ofroughness near the top of the bottom reflector 1100 than near the bottomof the bottom reflector 1100, although this is merely exemplary and infurther embodiments, the opposite is true (i.e., the roughened portion1102 is less rough near the top of the bottom reflector 1100 than nearthe bottom of the bottom reflector 1100).

The roughened portion 1102 may be formed by any suitable process orprocesses. In some examples, the roughened portion 1102 is formed bymechanical means such as abrading and/or thermal deformation, while insome examples, the roughened portion 1102 is formed by chemical meanssuch as chemical etching. In further examples, the roughened portion1102 is formed by a combination of both mechanical and chemical means.

Ridges and surface roughening are not mutually exclusive. In someembodiments, both techniques are used to control where reflected energyfalls on the substrate 102. FIG. 12 is a perspective view of a bottomreflector 1200 according to some embodiments of the present disclosure.The bottom reflector 1200 is suitable for use as the bottom reflector112 of the fabrication system 100 of FIG. 1 and/or any other suitablefabrication tool. For clarity, an outer portion 802 of the reflector1200 is represented as transparent to better illustrate an inner portion804. The outer portion 802 may be substantially similar to thatdescribed in FIG. 8 and may be structured so that thermal energy fromheating elements 108 is emitted between the outer portion 802 and theinner portion 804. In some such embodiments, the heating elements 108extend through holes in the outer portion 802 so that a portion of eachheating element 108 that produces the energy is disposed between theouter portion 802 and the inner portion 804.

Except where noted, the inner portion 804 may also be substantiallysimilar to that described in FIG. 8 and may have a substantiallycylindrical body 806 and a substantially frustoconical segment 808 thatflares outward extending from the substantially cylindrical body 806.The body 806 and the frustoconical segment 808, which may be made of anysuitable material such as silver, gold, and/or copper, may each beconfigured to reflect the thermal energy from the heating elements 108.The inner portion 804 includes a textured region 812 configured so thatreflected thermal energy is directed towards the substrate 102 and, inparticular, towards a circumferential region of the substrate 102. Thetextured region 812 includes circumferential ridges 812 substantially asdescribed in FIGS. 8-10 with a roughened texture substantially similarto the roughened portion 1102 of FIG. 11. Together, the ridges and theroughened texture are configured to direct the emitted energy tospecific locations on the substrate 102 (e.g., a circumferential regionnear the circumferential perimeter of the substrate 102).

The preceding disclosure provides a number of exemplary embodiments anda number of representative advantages. For brevity, only a limitednumber of combinations of relevant features have been described.However, it is understood that features of any example may be combinedwith features of any other example. Furthermore, it is understood thatthese advantages are nonlimiting and no particular advantage ischaracteristic of or required for any particular embodiment.

Thus, the present disclosure provides a system for thermal treatment ofa substrate that provides more uniform heating of the substrateundergoing a fabrication process such as epitaxy. In some embodiments,the system comprises a heating element, a substrate-retaining elementoperable to retain a substrate, and a reflective structure disposedbelow the substrate-retaining element. The reflective structure isoperable to direct thermal energy of the heating element towards thesubstrate retained in the substrate-retaining element and has a texturedportion where a texture of the textured portion is configured to directthe thermal energy towards the retained substrate. In some suchembodiments, the reflective structure includes a frustoconical segment,and wherein the textured portion is disposed on the frustoconicalsegment of the reflective structure. In some such embodiments, thetexture of the textured portion is configured to direct a portion ofthermal energy towards a circumferential region of the substrate.

In further embodiments, the thermal reflector comprises a cylindricalbody and a frustoconical segment extending from the cylindrical body.The frustoconical segment includes a textured region configured toreflect thermal energy towards a circumferential region of a substrate.In some such embodiments, the textured region includes an irregularlytextured surface configured to reflect the thermal energy towards thecircumferential region of the substrate. In some such embodiments, thetextured region includes a plurality of circumferential ridgesconfigured to reflect the thermal energy towards the circumferentialregion of the substrate.

In yet further embodiments, the fabrication system comprises a pluralityof heating elements disposed around a reflector and asubstrate-retaining element operable to retain a substrate. Thereflector includes a frustoconical portion having a textured surfaceconfigured to direct thermal energy of the heating elements towards thesubstrate retained in the substrate-retaining element. In some suchembodiments, the textured surface is irregularly textured with peaks andvalley of semi-random amplitude and frequency that are configured todirect the thermal energy of the heating elements towards the substrateretained in the substrate-retaining element. In some such embodiments,the textured surface has a plurality of circumferential ridgesconfigured to direct the thermal energy of the heating elements towardsthe substrate retained in the substrate-retaining element.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A system comprising: a heating element; asubstrate-retaining element operable to retain a substrate; and areflective structure operable to direct thermal energy of the heatingelement towards the substrate retained in the substrate-retainingelement, wherein the reflective structure has a textured portion, andwherein a texture of the textured portion is configured to direct thethermal energy towards the retained substrate.
 2. The system of claim 1,wherein the reflective structure and includes a frustoconical segment,and wherein the textured portion is disposed on the frustoconicalsegment of the reflective structure.
 3. The system of claim 1, whereinthe texture of the textured portion is configured to direct a portion ofthermal energy towards a circumferential region of the substrate.
 4. Thesystem of claim 1, wherein the texture includes a roughened irregularsurface configured to direct the thermal energy towards the retainedsubstrate.
 5. The system of claim 1, wherein the texture includes aplurality of circumferential ridge structures configured to direct thethermal energy towards the retained substrate.
 6. The system of claim 5,wherein a peak-to-trough height of the plurality of circumferentialridge structures varies along the textured portion.
 7. The system ofclaim 5, wherein a trough-to-trough width of the plurality ofcircumferential ridge structures varies along the textured portion. 8.The system of claim 5, wherein the plurality of circumferential ridgestructures has a peak-to-trough height of between about 0.1 mm and about2 mm
 9. The system of claim 5, wherein each ridge structure of theplurality of circumferential ridge structures has a roughened irregularsurface configured to direct the thermal energy towards the retainedsubstrate.
 10. The system of claim 1, wherein the system is an epitaxialdeposition system and wherein the reflective structure is operable todirect the thermal energy of the heating element towards the substrateduring an epitaxial deposition process.
 11. A thermal reflectorcomprising: a first portion; and a second portion extending from thefirst portion, wherein the second portion includes a textured regionconfigured to reflect thermal energy towards a circumferential region ofa substrate.
 12. The thermal reflector of claim 11, wherein the firstportion includes a cylindrical body; and the second portion includes afrustoconical segment.
 13. The thermal reflector of claim 11, whereinthe textured region includes an irregularly textured surface configuredto reflect the thermal energy towards the circumferential region of thesubstrate.
 14. The thermal reflector of claim 11, wherein the texturedregion includes a plurality of circumferential ridges configured toreflect the thermal energy towards the circumferential region of thesubstrate.
 15. The thermal reflector of claim 14, wherein the ridges ofthe plurality of circumferential ridges have varying peak-to-troughheights along the textured region.
 16. The thermal reflector of claim14, wherein the ridges of the plurality of circumferential ridges havevarying trough-to-trough widths along the textured region.
 17. Afabrication system comprising: a plurality of heating elements disposedaround a reflector; and a substrate-retaining element operable to retaina substrate, wherein the reflector includes a portion having a texturedsurface configured to direct thermal energy of the plurality of heatingelements towards the substrate retained in the substrate-retainingelement.
 18. The fabrication system of claim 17, wherein the texturedsurface is irregularly textured with peaks and valley of semi-randomamplitude and frequency that are configured to direct the thermal energyof the plurality of heating elements towards the substrate retained inthe substrate-retaining element.
 19. The fabrication system of claim 17,wherein the portion of the reflector is frustoconical portion and thetextured surface has a plurality of circumferential ridges configured todirect the thermal energy of the plurality of heating elements towardsthe substrate retained in the substrate-retaining element.
 20. Thefabrication system of claim 19, wherein circumferential ridges of theplurality of circumferential ridges are irregularly textured with peaksand valley of semi-random amplitude and frequency that configured todirect the thermal energy of the plurality of heating elements towardsthe substrate retained in the substrate-retaining element.